Scratched from one George Street show, Sandy Duncan returns in 'Circle Mirror Transformation'

Sandy Duncan stars as Mary, an acting teacher, in "Circle Mirror Transformation" at the George Street Playhouse.

Watch out for that vitamin D.

That’s the advice from Sandy Duncan, who took much more than the prescribed dose last spring.

“It turned out to be a big deal. Big. I’m dead serious,” says Duncan, 64, before realizing the cruel irony of using the adjective “dead.”

Her kidneys failed and her heart stopped. As a result, she had to drop out of “Creating Claire,” the play she was planning to open at the George Street Playhouse in New Brunswick.

But when you’re young at heart — and who more fits the description than Sandy Duncan? — you recover fast. So Duncan’s back at George Street, raring to go in Annie Baker’s “Circle Mirror Transformation” on Tuesday.

Duncan admits she’s not the star of “Circle Mirror.” “It’s completely an ensemble piece, where every actor is just as important as the others,” she says, before ticking off each on her fingers to ensure that all get proper credit: “Sandie Rosa; Amanda Sykes; Tom Riis Farrell, who comes to us from playing ‘Mr. Cellophane’ in Broadway’s ‘Chicago’; and Nick Wyman, who’s also the leader of our union (Actors Equity).”

Here, however, Duncan is the leader, in that she’s the teacher of an acting class. “Marty wants to bring people out of themselves. Not that this is in the script, but I have a feeling that Marty came from Oklahoma,” says Duncan, who grew up not that far away — in Tyler, Texas. “She went to college in the ’60s, became a yoga teacher and moved to Berkeley with some girlfriends and now has landed in Vermont, where she teaches this class. She’s not like those teachers who want to reduce their students to nervous breakdowns. Marty has no favorites and is very democratic and nurturing.”

That helps the plot. “It’s a play about self-discovery,” she says. “If you’re in a room together for six weeks, you learn things about other people.”

For those who fear the play will be too theater-centric for their tastes, Duncan insists otherwise. “It has less to do with theater and more to do with the silly things we put each other through,” she says. “It’s about trying to find meaning in our own lives. Watching the interpersonal relationships of these people is the fascination of it.”

If the play sounds overly talky, Duncan assures there are times it is not. “There are huge silences,” she says. “And isn’t silence one of the scariest things in our world? Even when people are silently texting, something’s going on. Here the silences can last for 30 seconds, which is a long time onstage.”

Duncan also has an interpretation of the title. “The ‘circle’ part refers to where people start and end up, but along the way they mirror each other and are transformed.”

The play runs only through the end of the month, but Duncan plans to be there for every performance. “What was horrible about what happened last spring,” she says, “is that I literally have never missed a show in my life, not in 52 years.” That includes her Broadway debut in “The Canterbury Tales,” her Tony-nominated performance in “The Boy Friend,” and her takeover stints during the runs of “My One and Only” and “Chicago.”

Most impressive of all is that Duncan never missed one of the 24 previews or 554 performances of “Peter Pan” on Broadway — which exceeded the total runs of the original production with Mary Martin and Cathy Rigby’s subsequent four revivals.

But Duncan says that when George Street artistic director David Saint assured her that he’d have her back, she believed him. “I didn’t expect to be playing a teacher,” she says, “but here I am.”

And has she ever taught or does she plan to? “Oh, good God, no,” she says. “I haven’t the patience.”